This study relates corpus-driven discourse analysis to the concept of collaborative knowledge construction. It demonstrates that the traditional synchronic perspective of meaning in corpus linguistics needs to be complemented by a diachronic dimension. The fundamental assumption underlying this work is that knowledge is understood not within the traditional epistemological framework but from a radical social epistemological perspective, and that incremental knowledge about an object of the discourse corresponds to continual change of meaning of the lexical item that stands for it. This stance is based on the assumption of the discourse as a self-referential system that uses paraphrase as a key device to construct new knowledge. Knowledge is thus seen as the result of collaboration between the members of a discourse community. The thesis presents, in great detail, case studies of asynchronous computer-mediated communication that allow a comprehensive categorisation of a wide range of paraphrase types. It also investigates overt and covert signs of intertextuality linking a new paraphrase to previous contributions. The study then discusses ways in which these new insights concerning the process of collaborative knowledge construction can have an impact on teaching methodologies.